384 The Microscope. 



color and the exquisite definition of the marginal as well as the 

 central portions of the field. I have been promised a loan of 

 one of these new eye-pieces, to tr}^ with my own objectives, and 

 if it shall prove to work as well with objectives of other makes 

 as with those of Spencer & Smith, I shall regard it as a real 

 advance in microscope construction. 



Incidentall}^ the subject of telescope construction came up, 

 and I was shown one — the new short-focus telescopes, the clear 

 aperture of which is 7-10 of an inch, and the total length over 

 all, when opened out for use, is only 6^ inches. It is easily car- 

 ried in the vest pocket, occupying a space of only four inches 

 in length by less than one inch in diameter, when closed. It 

 bears an eye-piece amplification of fifteen diameters, and with 

 this power gives a large field, with excellent definition and 

 ample light. 



I was sorry that Mr. Spencer had no samples of his highest 

 grade of homogeneous immersion objectives to show me, but 

 perhaps I had seen enough for one day, and I took leave of the 

 skillful young optician, well pleased with the man, his work, 

 and the simplicity of the mechanical means with which it was 

 produced. It would be a revelation to workers who believe in 

 the necessity for sub-stage condensers of large aperture, care- 

 fully centered and focused, to see the ease and certainty with 

 which the finest results were brought out with lamp and mirror, 

 only when manipulated with the proper knowledge and skill. 



The whole afternoon was entertaining, instructive and alto- 

 gether delightful to me, and I have thought best to give your 

 readers such share in my pleasure as they can glean from my 

 poor account of it. 



Dunkirk, N. Y. Geo. E. Blackham. 



From microscopical preparations, Heller estimates the number 

 of tubercle bacilli in the sputum of a tubercular subject at 

 1,000,000 per cubic centimeter; in a single expectoration, on an 

 average, 3,000,000 bacilli are discharged. — Wiener Med. Woch. 



